The mechanisms by which human receptors for immunoglobulin G constant regions (Fcgamma receptors) effect intracellular signal transduction will be studied by an approach emphasizing the use of recombinant vaccinia viruses to deliver genes encoding the receptors or receptor chimeras to functional effector cells. The receptor chimeras will be formed by genetic fusion of sequences encoding the extracellular domains of different leukocyte surface antigens to the transmembrane and intracellular sequences of human Fc receptors. Using cytolysis assays which depend on the ability of cells bearing Fc receptors to recognize and destroy antibody coated target cells, or which depend on the ability of cells bearing Fc receptor chimeras to recognize and destroy hybridoma cells expressing surface antibody binding to the extracellular portion of the chimera, we will investigate the Fc receptor sequences required for effective cytolysis, as well as the ability of different hematopoietic cell types to carry out cytolysis mediated by the different receptor isoforms.